1. Field of the Invention
This invention relates to a method for the manufacture of a high dropping point lithium complex soap thickened grease. More particularly, it relates to a method for carrying out the preparation of a high dropping point lithium complex soap thickened grease in a continuous operation including a continuous direct saponification step and a continuous dehydration step.
A lithium complex soap grease is one in which a mixture of lithium soaps of hydroxy monocarboxylic fatty acids and dicarboxylic fatty acids are employed as the thickener for the grease. The process of making a lithium complex soap grease having a high dropping point, i.e. over 500.degree. F., is a highly refined art. Small variations in the process are critical and can determine whether the grease resulting from the process has a high dropping point or not. For instance, the direct saponification of fatty acids by a lithium base has resulted in a lithium complex soap grease having a low dropping point, i.e. below 400.degree. F., and a poor appearance. Apparently, this is caused by the non-uniform dispersion of the soap of the dicarboxylic acid in the oil. Many prior art batch or non-continuous processes for preparing a high dropping point lithium complex soap grease employed alternative procedures to direct saponification.
2. Description of the Prior Art
U.S. Pat. No. 2,898,296 discloses a batch process for making high dropping point lithium complex grease which requires that the dicarboxylic fatty acid be converted to an ester prior to reacting it with lithium hydroxide.
U.S. Pat. No. 2,940,930, discloses a batch process for manufacturing high dropping point lithium complex soap grease which requires that a polyhydric alcohol or glycol be added to the monobasic and dibasic acid mixture before lithium hydroxide is reacted with the mixture.
U.S. Pat. No. 3,791,973 discloses a batch process for preparing a high dropping point lithium complex soap grease which requires the separate formation of the lithium soap of the hydroxy fatty acid and the lithium soap of the aliphatic dicarboxylic acid.
U.S. Pat. No. 3,689,242, discloses a batch process for preparing a high dropping point lithium complex soap grease which requires two distinct heating stages after saponification.
The novel process of the instant invention employs a continuous heating step to prepare a high dropping point lithium complex soap grease.
Continuous processes for manufacturing soap thickened grease compositions are disclosed in U.S. Pat. No. 3,475,335 and U.S. Pat. No. 4,297,227 but, no high dropping point grease have been made by these continuous processes.
The concurrently filed and copending application Ser. No. 385,744 discloses a batch process for preparing a high dropping point lithium complex soap grease which employs direct saponification requiring controlled alkali addition and only one heating stage after saponification.
In contrast to the prior art, a novel continuous process for making a lithium complex soap grease composition having a high dropping point i.e. above 400.degree. F., has now been discovered.